It is generally accepted that one way to ensure that catalytic converters for internal combustion engines fulfil the requirements for rapidly becoming active after starting the engine, is to provide a first converter close to the engine manifold, where the exhaust gas from the beginning has a high enough temperature to effect a light-off of the converter, and a second converter further down along the exhaust pipe where temperature and vibration are less demanding. Such divided converter systems are described in patents U.S. Pat. No. 5,444,978, EP 629 771, EP 761 939, and DE 44 42456. The extreme oscillations of pressure and temperature, as well as the high peak temperature make it difficult to get sufficient lifetime of the first manifold converter, and many suggested designs include means for easy replacement, or for bypassing it as soon as the second, main converter is operative, as shown in DE 44 42456.
The present invention is a new type of manifold converter and a way to mount it close to the engine, where the converter is less vulnerable to heat fluctuation and vibration, and where a rapid light-off is assured.
The converter and its mounting is described with reference to the figures, where FIG. 1 shows the configuration of the engine system, FIG. 2 a section through part of the engine and manifold with the manifold converter.
Catalytic converters usually comprise a monolith body with numerous parallel channels, the inner surfaces of which are coated with active catalyst layers. The monolith is commonly either an extruded ceramic body or a multiple of smooth and corrugated metal foils joined by brazing or welding. Ceramic bodies are brittle, however, and have to be elaborately mounted with resilient padding. Brazed or welded metallic monoliths develop large thermal stresses, and at their elevated temperatures there is a great risk of failure of welds or brazes.